Episode two of my experiment with the Raspberry Pi I have received at Pycon 2013. On the way back from Santa Clara I stopped by Fry’s and bought the only USB sound card they had in store, a weird looking Creative and a powered USB hub. I ordered also a case from Adafruit industries (not convinced of the case though).

The output of lsusb:

Bus 001 Device 006: ID 147a:e03d Formosa Industrial Computing, Inc.

Hooked them all together, installed avahi-daemon on the Pi so I can ssh into it easily from any lan (ssh raspberrypi.local, although I should change its name to something more unique). Tested arecord locally first. It took me a while to figure out how to use arecord, it’s old stuff that I’m not very used to. You need to specify the hardware device. If you get this sort of error:

arecord: main:682: audio open error: No such file or directory

probably you haven’t specified that you want to record from the card that actually has an input device

I hooked my phone’s audio player to the mic input of the USB card so that there would be constantly audio coming in the Pi, then started recording

pi@raspberrypi ~ $ arecord -D hw:1,0 -f s16_le -c 2 > test.wav

I have specified the hardware device I want to use, the format and the number of channels. Playing back that file worked.

pi@raspberrypi ~ $ aplay -D hw:1,0 test.wav

Next step was to capture live audio from the line input of the USB card, transcode that to OGG Vorbis and ship the bits to the remote Icecast server I setup last week. I quickly gave up on ezstream and started using ices2, the Icecast client: it seems easier to manage as it takes care of the encoding. This is the input module I used for the Pi:

And all seems to work: the Pi sends a clear signal up to the streaming server and it’s been doing that for a while. Big success so far. Next step for me will be to write a script that grabs data from the OpenStack Summit schedule for one room and adds that information as metadata for the streaming: this way the listeners will have an idea of who is speaking or what the session is about.

Update: the stream was having a wide latency, around 20 seconds so I decided to play a little bit with the sampling rates. The latency went down to around 1 second using <param name=”rate”>48000</param> in the input module and <samplerate>48000</samplerate> in the encode module, with no resampling. Unfortunately the USB card dies every now and then when not connected through a powered USB hub. Too bad, because the USB hub looks ugly.

Hi Stef,
thank you for your great report about Pi audio streaming…..
I’m completely new to this great world
I would like to know if you think the Raspberry Pi would be the right shield for my project.

I am a musician and sound designer, using Max/Msp, particularly interested on soundscape projects and researches, and this project is for an interactive sound installation in a real environment, with the sound produced by cicadas. As I’d prefer not to abandon a computer in a field, I assumed to use a microcontroller for this purpose.

So Raspberry Pi should be involved in steps 1-2-4-5 of the following:

1) sampling the sound locally produced by cicadas males during summer: mono signal is fine.
2) sending a stream of samples through the web in real time: Raspberry Pi should be connected to the web via 3G (no ethernet cable).
3) another computer placed in a studio should get this stream, making the audio treatments, re-sending it trough the web (splitted possibly into four independent synchronized channels-signals)
4) downloading the 4 processed streams;
5) distributing the sounds on a local multi speaker system, 4 channels basically.

If you think that all this is feasible through a Raspberry Pi plus a proper internet networking shield, I would buy it as soon as possible. Could you also tell me in case it would be possible with only 2 channels (stereo) playing?

I thank you very much for your attention, I stay waiting form an answer from you.

Hi Stefano, your project sounds interesting. I think you can do step 2 with the Pi but you’ll need to find a USB GPRS modem that supports ARM Linux drivers. I have no idea about that though. Also, I found the soundcard I bought not to be very stable: at times the driver seems to crash and the streaming stops. Unfortunately I have very little time to debug this. I’m considering shopping for a board that has native audio input and similar cost.

thank you for your interest!
yes I’ve to look for this USB GPRS modem that supports ARM Linux drivers……. maybe this will be the rock to climb…. I’, pretty sure you will find a more stable sound card…
I was wandering for arduino plus audio codec shields… but it seems that arduino has not enough resources to support both 3g shield and audio codec at the same time……
any way I’ll keep on studying the feasibility…

My first idea to stream audio would be to use pulseaudio’s network features. Have you thought about this? I’m looking to stream music from my laptop to 2 PIs in different rooms with hopefully not negligible latency.

I haven’t thought about pulseaudio since I was going to stream across the Internet I’ve assumed I needed something that took into account the latency. I may be wrong but I thought pulseaudio is designed more for LAN use than wider area network. Let me know how that experiment goes.

A better sound device (for RasPi and other uses), is the $25 Behringer UCA202.
I’ve been using those for years to record high quality audio to laptops, and it works fine on my Pi, too. I’ve only ever recorded about four hours at a stretch with it, but it didn’t drop out. (Powered by the Pi itself)

One problem I have had, is audio “skips” (I.E. If I was recording a song, I might jump from word 5 to word 8).
I think this is connected to arecord’s buffers and such, however, not the sound device.

I have always wanted to have a simple way to stream audio from the OpenStack Design Summits, much like Ubuntu used to do for its Ubuntu Design Summit. Since every participant to Pycon 2013 was kindly given a Raspberry Pi and having a couple of hours to kill, I have started playing with a simple idea: configure a Raspberry Pi to capture audio and stream it to a public icecast server.

First thing: spin up a virtual machine on a public cloud that will be serving as public icecast server. I have used my UniCloud account, created a small server, 512Mb ram, Ubuntu LTS 32bit. I updated the default security groups to allow traffic on port 22 (SSH) and 8000 (icecast), and I also needed to assign a public floating IP. Once the machine is up, simple apt-get install icecast2 took care of starting the audio streaming server. That’s it, streaming server part is done.

Back to the RasPi, in order to test the streaming server, I installed ezstream, copied the config files from /usr/share/doc/ezstream/examples. I copied ezstream_vorbis.xml to pi home dir:

Simple, rudimentary but I like because it seems to be easy. The next step for me is to buy a USB microphone to stream live audio captured in a room. The optimal configuration though is to use this system to stream audio easily from the OpenStack Summit rooms. I need a way to connect the USB input to a regular audio mixer: any idea on how to do that?

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